Add support for receiving USBTMC USB488 SRQ notifications via poll/select

Background:
In many situations operations on multiple instruments need to be
synchronized. poll/select provide a convenient way of waiting on a
number of different instruments and other peripherals
simultaneously.

Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index d77da2fd7b7053792543419ecbb30d64078ca7ee..867842951ea058ff43f2e8a4e0812402905847da 100644 (file)
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -27,6 +27,7 @@
 #include <linux/uaccess.h>
 #include <linux/kref.h>
 #include <linux/slab.h>
+#include <linux/poll.h>
 #include <linux/mutex.h>
 #include <linux/usb.h>
 #include <linux/usb/tmc.h>
@@ -1184,6 +1185,27 @@ static int usbtmc_fasync(int fd, struct file *file, int on)
        return fasync_helper(fd, file, on, &data->fasync);
 }
 
+static unsigned int usbtmc_poll(struct file *file, poll_table *wait)
+{
+       struct usbtmc_device_data *data = file->private_data;
+       unsigned int mask;
+
+       mutex_lock(&data->io_mutex);
+
+       if (data->zombie) {
+               mask = POLLHUP | POLLERR;
+               goto no_poll;
+       }
+
+       poll_wait(file, &data->waitq, wait);
+
+       mask = (atomic_read(&data->srq_asserted)) ? POLLIN | POLLRDNORM : 0;
+
+no_poll:
+       mutex_unlock(&data->io_mutex);
+       return mask;
+}
+
 static const struct file_operations fops = {
        .owner          = THIS_MODULE,
        .read           = usbtmc_read,
@@ -1192,6 +1214,7 @@ static const struct file_operations fops = {
        .release        = usbtmc_release,
        .unlocked_ioctl = usbtmc_ioctl,
        .fasync         = usbtmc_fasync,
+       .poll           = usbtmc_poll,
        .llseek         = default_llseek,
 };